Defects in neurotransmitter release, synthesis and storage are implicated in a number of diseases that include depression, Parkinson's disease and myasthenia gravis. Knowledge of the molecular mechanisms that underlie neurotransrnitter release will undoubtedly improve our ability to treat patients with these diseases. Three proteins have been found to be directly involved in the vesicular release of neurotransmitter: SNAP-25 (synaptosomal-associated protein of 25kDa), synaptobrevin (neuronal synaptobrevin (n-syb) in Drosophila), and syntaxin (syx). In vitro studies in both verterbrates and Drosophila have demonstrated that these three proteins interact to form a core complex by coil-coiled interactions of amphipathic helices. This complex is hypothesized to mediate the fusion of neurotransmitter-containing vesicles with the presynaptic membrane. In order to study the role of SNAP-25 in neurotransmitter release, our lab has recently generated a temperature-sensitive (ts) allele for SNAP-25 that results in enhanced neurotransmitter release. Using molecular, genetic and cellular approaches, the first phase of this proposal is aimed at uncovering the mechanisms that alter transmitter release in this SNAP ts allele. The second phase of this proposal involves the study of other ts paralytic mutations generated in our laboratory. The objective of this second study is to identify the gene responsible for the paralytic mutation and characterize its role in synaptic transmission.